Seasonal variation in amount and composition of monoterpenes emitted by young Pinus pinea trees - Implications for emission modeling

Current inventories of terpenes released from vegetation consider only the short-term influences of light and temperature on emissions to simulate tem poral variation during the year. We studied whole canopy emissions from you ng Pinus pinea during a 15-month enclosure in greenhouse chambers and exami ned data for other long-term influences. Mean daytime emission rates strong ly increased during spring, reached an annual maximum of approximate to 200 pmol m(-2) total needle area s(-1) (1.1 mu g g(-1) leaf dry weight h(-1)) between mid June and mid August, strongly declined in fall and reached an a nnual minimum of approximate to 1 pmol m(-2) s(-1) (0.006 mu g g(-1) h(-1)) between January and February. Normalization to standard temperature and li ght conditions did not change the annual time course of emissions, but redu ced summer to winter ratio from a factor of 200 to about 45. Seasonal varia tion was characterized also by changes in terpene composition: among the si x main compounds, three (t-beta-ocimene, linalool, 1.8-cineol) were exclusi vely emitted during sunlit hours in the main vegetation period, whereas the other (limonene, alpha-pinene, myrcene) were emitted day and night and thr oughout the seasons. The results suggest that different terpene sources in P. pinea foliage exist and that a great part of the annual emission course observed here results from seasonal influences on these sources. A global m odel to simulate plant emissions is proposed, which accounts for seasonal i nfluences on emissions in addition to the short-term effects of temperature and light. The model is tested on field data and discussed for its general application.